As video signals respectively including a luminance signal and two color-difference signals, for example, video signal respectively in a YUV422 format and a YUV420 format, which are transmitted by High Definition-Signal Digital Interface (HD-SDI) or the like, are present. In the video signals in the YUV422 format and the YUV420 format, resolutions of color-difference signals are different. The YUV422 format is a format implemented by taking color-difference samples relative to luminance samples at a ratio of 2:1 in a horizontal direction although the number of color-difference samples in a vertical direction is the same as the number of luminance samples. The YUV420 format is a format implemented by taking color-difference samples relative to luminance samples at 2:1 in both the vertical and the horizontal directions.
Input/output systems of devices used within a broadcasting station are integrated to transmit a video signal in the YUV422 format with HD-SDI. However, encoding/decoding apparatuses support only the YUV420 format in many cases. Accordingly, when a video signal is repetitively encoded and decoded to relay or edit a video, conversion between the YUV422 and the YUV420 is repeated within the apparatuses. Conventionally, there was a problem in that color-difference signals are significantly degraded by repetitively performing conversion between the YUV422 and the YUV420 as described above, leading to blurring of colors.
However, it is known that such a problem can be solved by selecting between a first low-pass filter for down-sampling used to convert between the YUV422 and the YUV420 and a second low-pass filter for up-sampling. Namely, by adopting filters that respectively satisfy a specified condition as first and second low-pass filters at all times, position shifts of color-difference pixels can be reduced to a minimum even if the above described conversion is repetitively performed.
Patent Document 1: Japanese Laid-open Patent Publication No. 2009-246929